As an individual ages, the eye is less able to accommodate, or bend the natural lens, to focus on objects that are relatively near to the observer. This condition is known as presbyopia. Additionally, for persons who have had their natural lens removed and an intraocular lens inserted as a replacement, the ability to accommodate is totally absent.
Among the methods used to correct for the eye's inability to accommodate is the mono-vision system in which a person is fitted with one contact lens for distance vision and one lens for near vision. The mono-vision system permits the lens wearer to distinguish both distance and near objects, but is disadvantageous in that a substantial loss in depth perception results. In another type of multifocal contact lenses, the optic zone of each lens of a lens pair is provided with more than one power. For example, the optic zone may have both distance and near power, which the eye uses simultaneously. Neither of these methods provides good results in terms of visual acuity and lens wearer satisfaction.
Lenses in which the power progressively and continuously changes from near to distance or distance to near vision power have been proposed. These lenses are advantageous in that they distribute light from viewed distant to near objects in a smooth fashion. However, when these lenses move on the eye so that the lens is not aligned with the center of the lens wearer's line of sight, visual artifacts, or ghosting of the image, results. By “ghosting” is meant that the object being viewed through the lens along with a faint image of the object is seen by the lens wearer. Thus, a need exists for a progressive design in which this disadvantage is overcome.